Nerve Growth Factor influences potassium movements in chick embryo dorsal root ganglionic cells

Recently we have shown that Nerve Growth Factor (NGF) influences the movement of Na⁺ across the membrane of chick embryo dorsal root ganglion (DRG) cells. When cell dissociates from 8-day embryonic chick DRG, equilibrated with ⁸⁶Rb⁺ (a K⁺ analog) in the presence of NGF, were transferred to NGF-free medium a marked loss of intracellular K⁺ occurred over several hours. The time course of K⁺ loss was similar to the time course of Na⁺ accumulation which occurs in the absence of NGF. NGF-deprived, K⁺-depleted DRG cells reaccumulated K⁺ within minutes of delayed NGF presentation, just as delayed NGF administration results in the rapid extrusion of Na⁺ from Na⁺-loaded cells. Restoration of K⁺ competence was dependent upon NGF concentration. The occurrence of this K⁺ response to exogenous NGF in other ganglionic preparations correlated with traditional responses to NGF in culture and previously observed Na⁺ responses. Neither the development nor the expression of the ionic defect (K⁺ depletion, Na⁺ filling) during NGF deprivation required the presence of both cations in the medium. NGF-dependent restoration of intracellular K⁺ in NGF-deprived chick DRG cells required the presence of intracellular Na⁺, and NGF-dependent extrusion of Na⁺ required extracellular K⁺. Thus NGF appears to influence the coupled (active) movements of Na⁺ and K⁺ across the membrane of its target cells, possibly by means of the classical Na⁺, K⁺-ATPase pump.